The present invention relates to a night vision monocular and, more particularly, to a night vision monocular equipped with a mechanism which enables to collimate the optical axis thereof within a predetermined image offset range, so as to enable to combine two night vision monoculars at random into an adjustment-free night vision binocular, and/or a locking mechanism for preventing permanent longitudinal and permanent lateral displacements of an image intensifying tube implemented therein.
Night vision devices are typically composed of a housing which houses an objective lens assembly at the distal end for collecting incident light, an eye piece lens assembly situated at the proximal end for displaying the light intensified image to the operator and an Image Intensifying Tube (IIT), situated between the objective lens assembly and the eyepiece lens assembly and which translates the collected photons to electrons and back to photons and thus intensifies the amount of light that reaches the eye.
First generation IITs are composed of a photocathode element which serves for collecting photon and for converting them into electrons. IITs further include phosphoranode element which is phosphorescent and thus reconverts the electrons into photons. Each step is characterized by signal amplification. Second generation IITs further include a multichannel plate (MCP) disposed between the photocathode and the phosphoranode and serves for further amplifying the electron signal obtained from the photocathode. The photocathode of third generation IITs contains Gallium-Arsenide (GaAs) which provides for improved sensitivity (i.e., conversion of photons to electrons ratio) and broader spectral range.
In some IITs, an additional component termed a fiber optic inverter is placed adjacent, and in close proximity, to a proximal end of the phosphoranode and is utilized for the reversion of an inverted image. Monoculars, which do not employ a fiber optic inverter, often utilize inverting lenses for inverting the image.
Night vision devices are widely used in the military to provide soldiers, aviators and sailors with the ability to passively view objects at night or during other low light conditions.
Night vision devices are traditionally manufactured as monocular assemblies or binocular assemblies depending upon the application being addressed. For instance, most night vision devices used by aviators and by soldiers operating vehicles are produced as binocular assemblies. This provides the operator with the needed depth perception during low light conditions. Examples of such night vision binocular devices are disclosed, for example, in U.S. Pat. No. 4,449,783 to Witte.; and U.S. Pat. No. 4,734,939 to Copp.
Monocular night vision devices often serve dedicated purposes, such as a gun sight or in combination with a camera lens, but there also exist many hand held "spotting scopes" used both commercially and by the military and law enforcement agencies. Examples of such monocular devices are disclosed, for example, in U.S. Pat. No. 5,084,780 to Phillips, U.S. Pat. No. 5,029,963 to Naselli.
Modular night vision systems, where independent night vision monocular assemblies can be selectively used by an operator to create a binocular device, also exist. Such assembled binocular devices are disclosed, for example, in U.S. Pat. No. 5,535,053 to Baril et al.
In monocular devices the incident beams of light are processed by the objective, IIT unit and the eyepiece. These optical elements are to be aligned with the optical path of the eye in what is known as self collimation. Unfortunately, perfectly collimated devices do not exist and thus misalignment of the optical elements with the optical path of the eye of the device creates a shift in the processed beams which thereby leads to a shift of the perceived image by an angle of 1-3.degree.. In monocular devices this shift dislocates image positioning as perceived by the operator.
Although this problem in monocular devices presents difficulties, it is readily corrected for by the adaptation of the operator. However when such monocular devices are incorporated to form binocular assemblies, the shift inherent to both monocular units creates a stereoscopic image which oftentimes is composed of converging, diverging or even dipverging images of the two monocular devices. This, in turn, produces a strain on the operators eyes and brain, as oftentimes the operator will try to correct for converging or diverging images by converging or diverging the eyes, respectively, while the human eye anatomy is not at all adapted for correcting for dipverging images.
This problem was partially addressed in aviation night vision integrated systems (ANVIS), e.g., by Litton (AVS-6, PVS-15) and ITT Defense & Electronics (AVS-9). In ANVIS, each monocular includes a single eccentric element implemented in the eyepiece assembly thereof. Such an eccentric element enables to shift the optical axis of its respective monocular with precision of several degrees, say 3-5.degree.. By co-adjusting paired monoculars, one can achieve optical axes adjustments (relative collimation) within a tolerance of delta 0.3-1.degree. for converging or diverging images and delta 0.3-0.5.degree. for dipverging images.
It is clear from the above description that monoculars of an ANVIS should be paired and only thereafter adjusted to achieve the reported tolerances. In other words, since the precision of adjustment of each monocular is relatively low, the co-adjustment of paired monoculars is essential for achieving the required tolerances.
It is further clear from the above description that optical axis adjustment is only relative and not absolute. Thus, pairing monoculars after adjustment is not possible, since such paired monoculars will clearly offset from the required tolerances.
Thus, ANVIS lack an effective mechanism for fine tuning for correction of divergent, convergent or dipvergent images of independent monoculars thereof, so as to enable to combine two night vision monoculars at random into an adjustment-free night vision binocular because self (as opposed to relative) collimation within a reasonable tolerance cannot be achieved for any of the monoculars.
There is thus a widely recognized need for, and it would be highly advantageous to have, a night vision monocular equipped with a mechanism which enables to self collimate the optical axis thereof within a predetermined image offset range, so as to enable to combine two night vision monoculars at random into an adjustment-free night vision binocular.
One additional limitation associated with prior art monoculars is the susceptibility to permanent lateral displacement of the IIT. This problem is of greater consequences for monoculars employed under rigorous conditions, such as those present in a battlefield.
A precise path of a collimated beam as created by monocular's components depends on the ability of all components to sustain a precise alignment with respect to each other, as shifts of these components, may lead to discollimation along with distortion or defocusing of the perceived image. Of the three optical components which are involved in light processing in monoculars, the image intensifier tube (IIT) is the most sensitive to movements and is often the major contributor to discollimation and defocusing due to lateral and/or longitudinal displacements, respectively. The problem is further intensified when the IIT unit employs a fiber optic inverter as described, which effectively doubles any lateral deviation from the true optical path.
To at least partially solve these problems prior art monoculars have resorted to anchoring the IIT to the device housing via a retaining ring supplemented with an O-ring which interface with the IIT, thus allowing for controlled recoverable movement of the IIT unit in response to shock. Although this solution is quite effective in preventing a permanent longitudinal displacement of the IIT unit, it does little in preventing lateral displacements thereof.
There is thus a widely recognized need for, and it would be highly advantageous to have, a night vision monocular that uses a mechanism for anchoring the IIT unit within a housing thereof, such that both permanent lateral and longitudinal displacements are reduced.